This invention relates generally to the injection of eggs, referred to as "in ovo" injection, and more particularly concerns an apparatus and method for the automated injection of various substances into eggs, especially for the control of disease in avian flocks.
There are a number of reasons in the fields of both medicine and poultry husbandry, among others, for the injection of a range of substances into various types of eggs. For example, in the field of medicine, fertile, or embryonated, eggs are used to incubate and harvest biologicals which have medical applications, such as certain vaccines. Eggs provide an appropriate environment for the growth of the vaccines.
Another reason for the injection of eggs is to add substances to the embryo or to the environment around the embryo. The purpose is to induce beneficial effects in the subsequently hatched chicks. The substances which may be added include antimicrobials such as antibiotics, bactericides and sulfonamides; vitamins; enzymes; nutrients; organic salts; hormones; adjuvants; immune stimulators and vaccines. This technique can, for example, lead to an increased percentage of hatch. The chicks from eggs that are injected prior to hatch may retain a sufficient amount of the injected substance so there is no need to inject the hatched bird. The chicks may grow faster and larger and experience improvement in other physical characteristics.
In ovo injection has also proven effective as a means for disease prevention. A significant problem in the poultry industry is a high incidence of infectious diseases which increases the cull rate and causes a high rate of mortality during the growing stage of young birds. An example is Marek's disease, which is a widespread herpes virus-induced lymphoproliferative disease of chickens. It is standard practice in commercial hatchery operations to immunize birds post-hatch against diseases like Marek's prior to placing them in brooder houses. This is a very labor-intensive process. With the advent of in ovo injection, certain types of vaccination, such as Marek's, which in the past had been carried out on hatched poultry are now successfully performed on embryonated eggs.
In general, the in ovo injection technique involves delivering a substance in fluid form to the interior of an egg using a needle. Occasionally, the needle is used to both penetrate the egg shell and deliver the fluid substances. However, fine needles, which are preferred when precise fluid delivery is required, may not be rigid enough to penetrate an egg shell. On the other hand, needles large enough and rigid enough to penetrate the egg shell may not provide suitable fluid delivery, both in terms of location and amount, which more delicate needles can provide. Furthermore, the penetrating process quickly dulls or plugs the needle. Therefore, a drill or punch is typically used to make a hole in the egg. Once the drill or punch has penetrated the egg shell, the needle is inserted into the interior of the egg for delivering the fluid substance.
An important parameter in in ovo injection is the location of the needle injection port within the egg at the time of fluid injection. Eggs are comprised of a brittle exterior shell and two flexible interior membranes. An outer membrane adheres to the interior of the shell and an inner membrane encases the fluid contents of the egg, including the allantois, amnion and yolk sac. At the time the egg is first laid, the two membranes are substantially coextensive. However, as the fertile egg is incubated, the inner membrane separates from the outer membrane, thereby forming an air cell between the two membranes, usually at the large end of the egg.
The egg can be injected at any location, and even into the embryo itself. The suitability of a particular location depends on the purpose for which the egg is being injected and the fluid substance delivered; since some substances must be delivered to a particular location within the egg in order to be effective. The problem with locating the needle at the appropriate injection point is that eggs vary in size. The resulting differences in distance between the shell and the location at which delivery of the fluid substance is desired complicates the task of consistently locating the injection point.
The amount of fluid delivered is also an important parameter. Typically, it is necessary that a sufficient amount of fluid be introduced into the egg to produce the desired effect. For example, in the case of bactericides, the amount of material introduced into the eggs must be sufficiently great to cause an appreciable increase in the percentage of hatch, but must not be so great that it kills or injures the embryos.
Automated apparatus and methods for injecting eggs are available. Generally, in such devices the eggs are brought under a bank of injectors housing needles and punches. First, the punches open a hole in the shell. Then the needle is inserted into the egg, followed by injection of fluid. A primary goal of automated in ovo injection is to be able to handle a high egg volume in a short period of time while consistently maintaining the amount and location of the fluid substance delivered within each of the eggs.
An automated device for injecting eggs must address the fact that eggs are not identical in size. Some devices include means for permitting vertical travel of the injectors relative to the apparatus to accommodate eggs of different sizes. However, another problem related to "in ovo" injection in commercial hatcheries is that the eggs are typically carried in setting trays, or "egg flats." Conventional egg flats comprise anywhere from 36 to 168 depressions for receiving the smaller end of the egg. Because the depressions are designed to accommodate the varying sizes of eggs, the eggs are free to wobble in the depression. As a result, the eggs may be slightly tilted with respect to the injectors. The capacity to accurately and precisely control the travel of a needle within the egg is diminished when the egg is tilted, even where the relative vertical travel between the egg and the needle is carefully controlled to account for differences in egg height.
Methods for dealing with the tilted eggs include lifting the eggs free of the flat in a suction cup integral with the injector to properly orient the eggs with respect to the needles or allowing the injectors to translate through an arc to properly orient the injectors to the tilted eggs. The former is impractical and has never seen commercial application. The latter method is somewhat effective, but can fail in practice when an injector translates improperly, becoming so angled with respect to an egg that the needle will glance off the egg shell, completely missing the egg. Therefore, fluid delivery location still remains a problem for automated in ovo injection devices.
Another problem with existing in ovo injection machines is that the pump mechanisms for delivering the substances may produce excessive sheer and compressive forces on the substance. In the case of Marek's disease vaccine, which is commonly presented as a whole-cell suspension, these forces can rupture the cells and thereby render the vaccine virus inside the cells much less effective.
Another consideration in egg injection is that it must be done in as clean an environment as is possible so that there is reduced probability of bacteria or mold entering the egg during or after puncture. Since the same needle is used repetitively, there exists the possibility of cross-contamination. Accordingly, the needle must be sanitized periodically. The magnitude of this problem is exacerbated in the automated apparatus where the same needle is used to inject hundreds of eggs.
For the foregoing reasons there is a need for an automated egg injection apparatus and method which is less labor-intensive than known systems. The apparatus should handle a high volume of eggs with a high level of precision with respect to both the location and quantity delivered. Ideally, the injection needle should be capable of functioning as both the penetrating and fluid delivery means. Fluid delivery should be gentle and precise so as not to damage live vaccine cells. The overall operation should be sanitary so as to minimize, if not eliminate, cross-contamination. The machine design should facilitate both manufacture and operation, thus reducing manufacturing and operating costs as compared to known devices and methods.